Annunciator circuit

ABSTRACT

An annunciation circuit is provided for an alarm signalling device, which annunciator causes a continuous indication of operation of the alarm signalling device after such operation. The indication is usually from a solid state light emitting device which is triggered from an SCR. The gate or driving circuit for the SCR is in series with a switch within the alarm signalling device, and is arranged to trigger the SCR only after the switch has operated. The SCR is in series with the solid state light emitting device and latches so that the light emitting device is maintained &#39;&#39;&#39;&#39;on&#39;&#39;&#39;&#39; until such time as power is temporarily removed from the circuit. A plurality of alarm signalling device may be powered from a single source and may operate a single alarm; and a simple visual inspection either of the annunciator board or of the devices themselves will show which device operated because the light or other annunciation will remain on until the SCR latch circuit is disconnected from its power source.

United States Patent 1 [111 3,866,194

Lawton Feb. 11, 1975 ANNUNCIATOR CIRCUIT [76] Inventor: Richard A.Lawton, 235 Cassandro 'm l Caldwell Blvd 717 Don Mills Ontario,Assistant Examiner-Richard P, Lange Canada 22 Filed: Mar. 21, 1973 [57]ABSTRACT An annunciation circuit is provided for an alarm sig- [211Appl' 343571 nalling device, which annunciator causes a continuousindication of operation of the alarm signalling device 52 15, 3 340 213340/2131 340/415 after such operation. The indication is usually from a340/248 R solid state light emitting device which is triggered [51] Int.Cl. G08b 23/00 from The gate driving Circuit for the SCR 5 Fidd f SearchN 340/213 R, 252 R, 25 is in series with a switch within the alarmsignalling de- 340/243 R 255 415 2131; 317/9 D 36 T vice, and isarranged to trigger the SCR only after the 200/1 7 switch has operated.The SCR is in series with the solid state light emitting device andlatches so that the [56] R f e Ci d light emitting device is maintainedon until such UNITED STATES PATENTS time as power is temporarily removedfrom the circuit. A plurality of alarm signalling device may be powered58 from a single source and may operate a single alarm; 3525988 8/I970Under n 340/4l2 and a simple visual inspection either of the annuncia-3:546:692 12/1970 Salzel. H 340/412 tor board or of the devicesthemselves Wlll show which 3.543399 12/1970 Monigal et alm 340/415device operated because the light or other annuncia- 3,688,294 8/1972Erpelding 340/415 tion will remain on until the SCR latch circuit isdis- 3,696,364 10/1972 Lavelle 340/213 R connected from its powersource. 3,706,087 12/1972 Berns 340/213 R 3,706,088 l0/l966 Jorgenson340/213 R 3 Clams, 2 Drawlng Flgures PMENTEBFE H915 3866,19 1

ALARM FIG I ANNUNCIATOR CIRCUIT FIELD OF THE INVENTION This inventionrelates to alarm signalling devices; and particularly to annunciator orindicating circuits therefor which provide a continuous indication ofthe operation of an alarm signalling device. The circuits provided bythis invention are particularly useful in such alarm signalling devicesas rate-of-rise of temperature and/or maximum or minimum temperaturesensing devices; and the invention may equally be useful in other suchdevices as over speed sensors, flow sensors, etc.

BACKGROUND OF THE INVENTION As noted, this invention is particularlyuseful in such installations of alarm signalling devices as thermaldevices which may signal a rate-of-rise of temperature in excess of apredetermined rate, or a temperature in excess of a predeterminedtemperature, etc. Such devices are very often found in large industrialor public buildings. Very often an installation of a plurality ofthermal detectors of the sort usually found in such buildings mayinclude a number [up to a dozen or more ]of like devices which areconnected to a single alarm circuit. For example, all of the devices ona floor or a group of floors of a building, or in a particular area of abuilding, may be connected to a single alarm circuit. Operation of anyone of the devices causes an alarm signal to be given, at such receivingstations as central watch stations, police or fire departmentheadquarters etc. Likewise, a plurality of other types of sensors oralarm signalling devices may be used in buildings, industrial processes,etc., where several devices may be connected to a single alarm circuit.In all such circumstances, however, whan an alarm is given especially inresponse to a transitory alarm condition, or as a result of a temporaryfault it is usually not possible to determine which one of the alarmsignalling devices has caused the alarm signal to be activated. Thus, anindividual-inspection of each alarm signalling device may be required todetermine which device cause the alarmsignal.

In such installations as thermal detector installations where aplurality of like temperature and rate-of-rise devices which may, infact, be the same devices each having the ability to trip or cause analarm under either or both of two pre-set alarm conditions, there may beintermittent operation of one of the devices which may be false in whichcase, the device is faulty or which may be as a result of transitorytemperature rise or maximum temperature conditions in excess of thepermitted limits, but which may last for a period of only a few seconds.Nevertheless, an alarm signal would have been caused; and in suchcircumstances it may be very helpful to know which of the devices hasoperated. If the device itself is faulty or set to operate at limitswhich are too low, it may be very difficult to discover such device. Itis therefore desireable than an annunciation or indication be giveneither at an annunciator board or at the device itself whenever thedevice operates to cause an alarm signal; and that such annunciavices onthe same alarm circuit. Power for operation of the device may be derivedfrom the alarm circuit, or independently, as discussed hereafter.

During the installation, it is helpful to be able to test the operationof an alarm signalling device; and to check the continuity of the alarmcircuit. Likewise, it is helpful in two-wire alarm circuits to make eachpower utilization device to be polarity insensitive: i.e., so that eachdevice, especially a solid state circuit, which may operate no matterwhich direction the impressed voltage across such device may be. Indeed,it may be contemplated that in certain conditions, alarm signallingdevices may be desired to have annunciators associated therewith whichwould operate with an AC voltage impressed across them rather the theusual DC voltage. It should be noted that most such alarm signallingcircuits operate at a low DC voltage, which is easier to handle than ahigh voltage, and which can assure better quality power than low voltageAC which might be subject to waveform or other distortion. In any event,it may happen that a technician, when installing a plurality of alarmsignalling devices in a two-wire alarm circuit, might accidentallyreverse the polarity of connection of one device relative to another.

It is desirable to provide an annunciator or indicator circuit which hasthe smallest possible physical volume, so that it may be installedeasily in the base or container of an alarm signalling device, and whichprovides circuit reliability and assurance of operation over a longperiod of time. Thus, the present invention is particularly related toannunciator circuits for alarm signalling devices where the annunciatorcomprises a light emitting semi-conductor device usually, a lightemitting diode in series with a gating and latching device. The gatingand latching device which is usually employed in such circuits is asynchronous switch operable from a gate circuit which in turn is firedfrom a control circuit. The most common of such device is a siliconcontrolled rectifier (SCR). An SCR is also a device which latches; i.e.,once the SCR closes so that it becomes conductive, it will not re-openuntil power if removed from the cathode-anode circuit of the SCR. Thisis especially important in such circumstances as those discussed above,where an alarm signalling device may have intermittent operation whichcauses the opening or closing of a single-pole switch. After such aswitching operation, an SCR which is fired or turned on in response to acontrol circuit which in turn is responsive to the switching operationwithin the alarm signalling device, then provides a latching function toassure the continuing indication of the fact that a switching operationhas taken place.

Several different control circuits which control the gate of an SCR arecontemplated by this invention. They include a voltage dropping networkto provide sufficient gating and latching voltage for an SCR, in serieswith a circuit having a time delay (for DC operation, a parallel RCcircuit) so as to avoid inadvertent operation due to external fieldconditions such as transient voltages, radio frequency interference,etc., and a transistor circuit which is operative to gate the SCR to itslatched condition only after the occurrence of a switching operationwithin the alarm signalling device.

BRIEF SUMMARY OF THE INVENTION It is an object of this invention toprovide an annunciator circuit for an alarm signalling device, which maybe installed either within the device or at a remote annunciator board,and which provides a continuous indication of the fact that the alarmsignalling device with which the annunciator is associated has caused analarm signal to be given by its own operation.

Another object of this invention is to provide a lowpriced, solid stateannunciator for use with an alarm signalling device, where theannunciator circuitry is physically quite small.

Yet another object of this invention is to provide an annunciator devicethat gives a continuing like indication of the fact that a switchingoperation has taken place in an alarm signalling device, where suchindication is continued until power to the annunciator circuit is atleast temporarily interrupted.

A still further object of this invention is to provide a low powerutilizing annunciator device for use with alarm signalling devices, asspoken of above.

BRIEF DESCRIPTION OF THE DRAWINGS These and other features and objectsof the present invention are more fully described hereafter inassociation with the accompanying drawings, in which:

FIG. 1 is a circuit of a preferred embodiment. of an annunciator devicein accordance with this invention and FIG. 2 is a circuit of analternative preferred embodiment of an annunciator device in accordancewith this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS As noted above, an alarmsignalling device such as a thermal device which causes an alarm signalto be actuated either upon the sensing by the device of a rate-ofchangeof temperature faster than a predetermined rate, or upon the sensing ofa temperature higher (or lower) than a predetermined temperature, may beconnected to an alarm circuit together with a plurality of like devices.Each of those devices is therefore a switching device, and an alarmcondition causes a change of the switch condition of at least a singlepole of a switch within the device. In the usual installations, theswitches within alarm sensing devices are normally open switches, sothat when the devices are monitoring but not in alarm status, there islittle or no current or power consumption. Normally closed switches may,however, by used to provide an indication at a power source of thecontinuing operation of the circuit in monitoring or standby condition.

FIG. I shows a circuit in accordance with this invention, having inputterminals 10 and 12 which are connected to the input terminals of adiode bridge indicated generally at 14. The output terminals of thediode bridge 14 are indicated at 16 and 18, being the positive andnegative output terminals of the diode bridge, respectively. Obviously,the power source to which terminals l and 12 may be connected cancomprise an alarm circuit where the alarm signalling device includesonly a single-pole single-throw switch, as discussed hereafter. Thecircuit to which terminals and 12 are connected may have an AC or a DCvoltage across it, and either of terminals 10 or 12 may be connected tothe positive side or the negative side of such circuit when it is DC. Inany event, the output terminals of the diode bridge 14 provide apolarized DC; so that the entire circuit is insensitive to polarity ofthe power source at terminals 10 and 12. For purposes of thisdiscussion,

however, the power source for the circuit to be discussed hereafter maybe considered to be the positive and negative terminal 16 and 18,respectively of the diode bridge 14.

Likewise, a capacitor 20 may be connected between input terminals 10 and12, for extreme noise suppression of noise on the input power lines ifnecessary.

A switch 22 is shown in FIG. 1, with one side thereof connected to thepower source in this case, terminal 16 of diode bridge 14. As noted,switch 22 may be a single-pole single-throw switch, leaving aside anyconsideration of another pole of the switch which is discussed hereafterwith respect to an alternative embodiment of the circuit of FIG. 1.Switch 22 is the switch within the alarm signalling device whoseswitching operation causes an alarm signal to be activated. However, asnoted above, the operation of the switch 22 may be transitory, as aresult of alarm conditions which occur for only a very short period oftime, faulty operation of the alarm signalling device per se, or forother reasons. Thus, the circuit of FIG. 1 is provided to cause anannunciation or indication of a switching operation of the switch 22,unless that switching operation is for a very short time which is lessthan the time constant of an RC circuit to be discussed hereafter; andeven though the switch 22 may restore to its standby condition, theannunciation will continue.

The annunciator which is most commonly used is a light emitting diode24; although other lamp means or annunciator means such as relays, etc.,may be used. In series with the light emitting diode 24 is a resistor 26whose function is to limit the operating current to the light emittingdiode 24 upon activation of the annunciator operation of the circuit. AnSCR 28 is also in series with the light emitting diode 24; and thecathode side of the SCR may be connected to the negative side 18 of thediode bridge 14.

A resistor 30 is in series with the switch 22, and the side of resistor30 which is remote from the switch 22 i.e., junction 32 is connected tothe gate of SCR 28. A further resistor 34 is connected in series withresistor 30 from junction 32 to terminal 18 of diode bridge 14; so thatresistors 30 and 34 may form a voltage divider string. A capacitor 36 isarranged in parallel with resistor 34 to form an RC circuit, whose timeconstant is determined by the values of the capacitor and resistorwithin the circuit.

The operation of the circuit as it has been described so far, is asfollows. If switch 22 closes, capacitor 36 begins to charge, and if theswitch 22 remains closed for a longer time than the time constant of theRC circuit 34, 36 so that capacitor 36 becomes fully charged, thevoltage at junction 32 between resistors 30 and 34 become such as tofire SCR 28 to make it conductive. The values of resistors 30 and 34 arechosen having regard to the usual operating circuit voltage, the firingvoltage required for SCR 28, etc. When SCR 28 fires and becomesconductive, current flows through current limiting resistor 26 and thelight emitting diode 24. Thus, the light emitting diode causes anannunciation or indication of the fact that a switching operation ofswitch 22 has occurred. As noted previously, the light emitting diode 24may be replaced with other current operated devices such as relays,small lamps, etc., whose operation and indication would continue only solong as current continued to flow through such indicating devices. If,at any time after the SCR 28 has fired, switch 22 opens once again,there will be no effect on the circuit because the SCR would remainlatched i.e., conducting and the light emitting diode 24 would continueto be operative. Obviously, the only way that the annunciator orindicator can become non-operative is to at least temporarily remove thecircuit from the power source. This may conveniently be achieved byopening a normally closed switch such as switch 38.

If the switch 22 is ganged as one pole of a singlethrow switch havingmore than one pole, such as to switch 40 in FIG. I, the operation of thecircuit remains essentially as discussed above, except as follows.Either switch pole 22 or switch pole 40 may be the switch within thealarm signalling device whose operation is predicated on the existenceof an alarm condition. The other of the poles of the switch is ganged sothat, in this case, a two-pole single-throw switch is achieved. Switch40 may be connected to an alarm circuit 42, whose nature is not relevantto this invention. In any event, it is now seen that the power sourcefor the alarm circuit is independent from the power source for theannunciator circuit including the light emitting diode 24, SCR 28 andthe control circuitry therefor. Operation of the annunciator circuit istherefore independent of any fault condition e.g., an open circuit whichmay occur in the alarm circuit. Similarly, operation of the detector andannunciator circuitry maybe proven, and continuity at least of theannunciator circuitry proven, without causing an alarm signal to begiven such as at a central control receiving station, by suitablemanipulation at the device itself.

An alternative embodiment of an apparatus according to this invention isillustrated in FIG. 2, where like numerals indicate like circuitelements. In the circuit of FIG. 2, the collector of a transistor 44 isconnected at junction 46 to the gate of SCR 28. Also connected tojunction 46 is a resistor 48. Resistor 48 and a resistor 50 are eachconnected to terminal 16 of the diode bridge 14, and the other side ofresistor 50 is connected to the base of transistor 44. Switch 22 is alsoconnected, in this instance to the base of the transistor 44, and toterminal 18 of thediodebridge 14.

In the same manner as discussed above, the switch 22 may be one pole ofamultiple-pole single-throw switch.

In the circuit ofFIG. 2, where switch 22 is a normally open switch, thetransistor 44 is maintained in its con ducting state by the voltageacross it, as seen at its base from resistor 50. The voltage at junction46, and thus at the gate of SCR 28, is such that the SCR remains openand nonconductive. However, when switch 22 closes, even temporarily, itcauses a base to emitter short circuit on transistor 44, thereby turningtransistor 44 off so that it become non-conductive. The voltage atjunction 46 therefore tends to go upwards to the voltage at terminal 16,or at least until the firing voltage of SCR 28 is reached whereupon theSCR fires and latches. The voltage at junction 46 thereafter collapses.

If switch 22 in FIG. 2 is opened after it has been closed and SCR 28 hasfired, the SCR remains latched in the same manner as discussed above,and the light emitting diode 24 or other such annunciator device as maybe used continues to indicate the fact that the switch 22 has at leastmomentarily been closed. Restoration of the circuit of FIG. 2 to itsstandby i.e., nonindicating status is, once again, accomplished by suchmeans as temporarily opening switch 38. The circuit of FIG. 2 is suchthat when the annunciator is in its non-indicating status, a certain butvery low power consumption will occur because of the conducting statusof transistor '44. If switch 22 is replaced with one which is normallyclosed, the operation of the circuit of FIG. 2 can be duplicated bysuitably reconnecting the transistor 44.

It will be noted that the SCR 28 or other synchronous switch which maybe fired by operation of the control circuit, and which latches isoperable only upon the operation of a suitable control circuit which is,itself, active so as to control the firing of the SCR only after aswitching operation of the switch within the alarm signalling device.Thus, switch 22 causes a control circuit which includes resistor 30 anda parallel circuit 34, 36 to fire the SCR 28 in the circuit of FIG. 1;whereas in the circuit of FIG. 2, a switching operation by switch 22causes transistor 44 to turn off, thereby raising the voltage at thegate of SCR 28, and causing the SCR to fire. In both circuits, once theSCR 28 has fired, the light emitting diode 24 which acts essentially asa short circuit when it is conducting remains on, because of thelatching operation of the SCR, until such time as power is removed atleast from that portion of the circuit which includes the light.emitting diode and the SCR in series. I

Various alternative embodiments, and additions thereto by way ofcomplementary or electrically isolated power circuits, have beendiscussed. Various types of control circuitry which causes the SCR tofire only after a switching operation of the switch within the alarmsignalling device which causes an alarm signal to be generated, havebeen discussed, as well as various alternatives of current operationannunciator devices. It has been noted that the circuits of thisinvention-can operate without regard to the polarity of the power sourceto which the circuits may be connected; and it has been noted thatespecially with the use of all solid state components, powerconsumption'and physical size as well as costs can be kept at a minimum.

Various other amendments, alterations or :substitutions may be made tothe circuits taught herein, without departing from the spirit and scopeof the appended claims.

What'l claim is a 1. In an alarmsignalling device having at least asingle-pole single-throw switch whose operation is determined by achange of ambient conditions being monitored by said device, and wheresaid switch is connected in series with one side of a source ofelectrical power; the improvement comprising annunciator meansassociated with said alarm signalling device and connected to said powersource to provide a continuous annunciation after a switching operationof said switch in response to a change of the conditions being monitoreduntil such time as said annunciator means is at least temporarilydisconnected from said power source, including;

annunciator means operable from said power source and in series withgate means; said gate means being operable only upon operation of acontrol circuit therefor; said control circuit being active to controlsaid gate means only after a switching operation of said switch;

said gate means including latch means connectedto said power source tomaintain said gate means.

7 8 until said latch means is disconnected from said switch saidtransistor become non-conductive and power urc Said g and latch meansbeing an said SCR is fired by the voltage then impressed on SCR, andsaid annunciator means being a light the gate h f Fmming dloflei 2. Thecircuit of claim 1 where said power source is said control circuit forsald gate means from hav ng the output terminals of a diode bridge atranslsmr whose base is connected senes wnh 3. The circuit of claim 1where said detector device said switch; resistor means connected to biasthe base of said transistor so that said transistor is conhas at least atwo'pole smgle'throw sw'tch whose Opel" ductive when said switch is inits normal switching is determined and Controlled at only one polecondition; and further resistor means connected at thereof, and wherethe Second P of said Switch is one end both to said transistor and tothe gate of nne ted o an alarm Circuit. said SCR, so that after aswitching operation of said

1. In an alarm signalling device having at least a single-polesingle-throw switch whose operation is determined by a change of ambientconditions being monitored by said device, and where said switch isconnected in series with one side of a source of electrical power; theimprovement comprising annunciator means associated with said alarmsignalling device and connected to said power source to provide acontinuous annunciation after a switching operation of said switch inresponse to a change of the conditions being monitored until such timeas said annunciator means is at least temporarily disconnected from saidpower source, including; annunciator means operable from said powersource and in series with gate means; said gate means being operableonly upon operation of a control circuit therefor; said control circuitbeing active to control said gate means only after a switching operationof said switch; said gate means including latch means connected to saidpower source to maintain said gate means closed and said annunciatormeans operative even after a further switching operation of said switch,until said latch means is disconnected from said power source; said gateand latch means being an SCR, and said annunciator means being a lightemitting diode; said control circuit for said gate means from having atransistor whose base is connected series with said switch; resistormeans connected to bias the base of said transistor so that saidtransistor is conductive when said switch is in its normal switchingcondition; and further resistor means connected at one end both to saidtransistor and to the gate of said SCR, so that after a switchingoperation of said switch said transistor become non-conductive and saidSCR is fired by the voltage then impressed on the gate thereof.
 2. Thecircuit of claim 1 where said power source is the output terminals of adiode bridge.
 3. The circuit of claim 1 where said detector device hasat least a two-pole single-throw switch whose operation is determinedand controlled at only one pole thereof, and where the second pole ofsaid switch is connected to an alarm circuit.